A conventional cornice board is typically constructed of an elongated horizontal wooden panel with side panels extending between the panel and the wall, in order to enclose or "box in" curtain rods at the upper ends of a window frame. Most commonly, the boards are covered with fabric of a texture and color or pattern which is felt to provide the most pleasing appearance. Materials other than wood are known to also have been used as cornice boards. For example, in U.S. Pat. No. 5,361,821, an elongated cornice made of semi-soft foam is slit along its back side and is supported on a stiffening plate which enters the slit. The foam is then covered with fabric through a wrap and tuck process. U.S. Pat. No. 5,345,990 illustrates foamed polyurethane with undulated mounds or curves, and slits between adjacent curves into which slits the fabric is tucked. In yet another U.S. Pat. No. 5,505,245, a resilient foam body is suspended from a horizontal curtain rod assembly. It too has slits for fabric-tucking purposes. More recently, there has been observed in a television infomercial a cardboard cornice which is attached to the back side of a soft foam elongated cornice. Together, the thin, apparently relatively flimsy cardboard and the foam piece or pieces are presumably of sufficient strength to maintain them relatively straight once fabric has been tucked into slits provided on the face and between the cardboard and the foam along the back. It would appear that use of this last-mentioned construction would be limited to shorter cornice lengths such as would cover standard double-hung window frames. While it is not clear from what has thus far been observed, it is believed that this latter design would be inadequate for a wide picture window of six feet or more in width, for example. It is not known whether it has been taught that one can selectively pin or similarly attach removable decorative objects to fabric-covered soft or semi-soft foam cornice boards to create special effects. This has been done with some padded wood frame cornice boards, where mention is made of attaching objects such as butterflies or flowers. (See U.S. Pat. No. 5,159,965). Another method which might possibly be considered decorating of a limited nature is to provide pouches for storing items by hanging them from curtain rods. This is shown in U.S. Pat. No. 5,785,188. Despite the volume of effort given to cornice treatment, no one appears to have provided a simple board structure that is self-sustaining without sag throughout and independent of its length, that is also capable of easy adjustable mounting to a supporting surface and that enables easy pinning of objects to its outwardly-facing side to provide an aesthetically pleasing appearance.